1. Field of the Invention
This invention relates to coated textile fabric used in the manufacture of inflatable devices such as air bags, side air curtains or the like, for vehicle occupant restraint systems. More particularly, the invention relates to woven or knitted textile fabrics coated with a plurality of polymeric layers that impart superior air holding and heat sealable properties to the fabric. The polymeric coatings of the invention form a bead when heat sealed, thus providing a reinforced heat seal bond that permits the manufacture of preformed air holding channels and/or side air curtains that will withstand the explosive pressure of inflation gas when the air bag is deployed.
2. Description of the Related Art
Present restraint systems for automotive vehicles include driver and passenger side air bags that are instantaneously gas-inflated by explosion of a pyrotechnic material at the time of a collision to provide a protective barrier between vehicle occupants and the vehicle structure. Much of the impact of a collision is absorbed by the air bag, thus preventing or lessening the possibility of serious bodily injury to occupants of the vehicle. Air bags are located, typically, in a collapsed, folded condition housed in the steering wheel, to protect the driver, and in the dashboard, to protect a passenger seated next to the driver. Recently, the automotive industry has introduced air bags that are stored in the back of the front seats or in the rear seats to protect the cabin occupants in the event of a collision occurring on either side of the vehicle. More recently still, another safety feature that has been made available for passenger vehicles, especially the so-called sport utility vehicles or SUVs, includes side-impact protective inflatable side air curtains designed to provide a cushioning effect in the event of side collisions or rollover accidents. These side air curtains are stored uninflated in the roof of the vehicle and, in the event of a collision, deploy along the interior side walls of the cabin of the SUV.
Each of these various types of air bags and side air curtains has distinct design and physical property requirements, such as gas (air) holding permeability, air pressure and volume control, and puncture resistance. For example, driver side air bags, which inflate and deflate almost immediately thereafter, must have little or no permeability. Passenger side air bags, on the other hand, require a controlled permeability. Moreover, all such vehicle air restraint devices must have superior packageability and anti-blocking qualities. Packageability refers to the ability of a relatively large device such as an air bag to be packaged in a relatively small space as, for example, within a steering wheel. Anti-blocking refers to the ability of the device to deploy practically instantaneously without any resistance caused by the material sticking to itself, particularly after being stored for relatively long periods of time before it is deployed. These and other properties are determined in large part by the type of fabric used, whether it is knitted or woven, and most importantly, the nature of the coatings that are used on the fabric.
The air holding capability of side air curtains is critical since these safety devices must remain inflated for an extended period of time to protect passengers in multiple rollovers. Unlike air bags which are designed to inflate instantaneously, and to deflate almost immediately after inflation in order to avoid injury to the driver and front seat passenger, side air curtains used in SUTs, or in ordinary passenger vehicles, must be capable of remaining inflated in the range of from about three (3) to about twelve (12) seconds, depending upon the size of the air curtain and the size and type of vehicle involved. An average passenger vehicle would require a side air curtain of from about 60 inches to about 120 inches in length as measured along the length of the vehicle. A larger vehicle, such as a minivan, would require an even longer side air curtain. The maximum inflation period of a side air curtain should be sufficient to protect the cabin occupants during three (3) rollovers, the maximum usually experienced in such incidents.
When side air curtains are deployed, they may be subjected to pressures within a relatively broad range, depending upon their specific location or application. For example, air bag deployment pressures are generally in the range of from about 50 kilopascals (kpa) to about 450 kpa, which corresponds generally to a range of from about 7.4 psi (pounds per square inch) to about 66.2 psi. Accordingly, there is a need for fabric products and air bags which can be made to be relatively impermeable to fluids under such anticipated pressures while being relatively light in weight.
One means of improving air holding capability in vehicle restraint systems has been through coatings such as chloroprene and silicone rubber coatings, applied to the textile (e.g., nylon) substrate. U.S. Pat. No. 5,110,666 discloses a woven nylon substrate coated with polyurethane to provide the desired permeability and retention of inflation gas. Nevertheless, wherever coated fabrics are used the problems of controlling air permeability, air pressure and volume remain. Additionally, in the manufacture of air bags in which stitching is used to form the bag structure, each stitch creates a potential leak that adversely affects the integrity and air holding capability of the bag, especially when instantaneous deployment of an operative bag is required. Insufficiency of adhesion of the coating to the fabric substrate also is a serious problem that must be addressed. For example, the smoother the substrate surface, generally the more difficult it is to obtain strong adhesion of the coating material to the substrate. With some coatings such as silicone rubber (polysiloxane), radio frequency (RF) heat sealing techniques cannot be used to form the air bag because this material will not flow at heat sealing temperatures. In such instances, air bags are usually made by stitching, a process which requires the addition of an adhesive sealant, ultrasonic weld, RF weld or other type of fusion process in the stitched areas. Even so, as noted, leakage of air may occur at the stitching, which lessens the protective capability of the air bag.
There have recently been developed improved polyurethane, acrylic, polyamide and silicone coatings that are coated in layers on the fabric substrates. It has been found that adhesion characteristics are greatly improved with such layered coatings. Examples of such coated fabrics and methods of coating such fabrics are disclosed in commonly assigned applications Ser. No. 09/327,243, now U.S. Pat. No. 6,239,046, Ser. No. 09/327,244, and 09/327,245 both abandoned, filed Jun. 7, 1999, the disclosures of which are incorporated herein by reference and made a part of this disclosure.
U.S. Pat. No. 5,863,644 discloses woven or laid structures using hybrid yarns comprising reinforcing filaments and lower melting matrix filaments comprised of thermoplastic polymers to form textile sheet materials of adjustable gas and/or liquid permeability. During the formation of textile fabrics in accordance with the disclosure, polyester fibers in the weaves are melted by the application of heat to form textile sheet materials that are stated to have predetermined gas and/or liquid permeability. I have invented a coated textile fabric for air holding devices in inflatable vehicle restraint systems which can be heat sealed to withstand inflation pressures in a controlled and improved manner and without stitching.
It has been found that a textile fabric substrate, when coated with a multi-layered polymeric coating, including a composite coating layer of polyurethane polymer and polysiloxane. Preferably a suitable adhesion promoter and filler such as epoxy resin is added to the composite coating layer. The composite layer facilitates the formation of a sealing bead when heat sealed with a similarly coated fabric, to provide a reinforced heat seal bond. The exceptional bonding properties thus obtained permit the manufacture of an air bag or side air curtain with preformed air holding channels that will be able to withstand the pressure of inflation gas without the need for stitching.
The coatings of this invention can be applied directly onto the textile substrate itself or indirectly by transfer coating to a coated carrier sheet. Multiple reinforced seals can be generated with a bead effect by means of a RF (radio frequency) heat sealing bar having predesigned bead cavities in the die. During the heat sealing process the components that together comprise the composite coating layer of the invention flow at different temperatures, thus creating a bead in the preformed die cavity design. In this process, when heat is applied in a predetermined temperature range, the polyurethane polymer flows into the preformed cavity of the die, thus creating a bead, while the polysiloxane does not flow at the heat sealing temperatures utilized. Vulcanization of the polysiloxane takes place at the time of, or immediately after formation of the bead to bond the polymeric layers together. In addition to its major components of polyurethane and polysiloxane, in the preferred embodiment the composite coating layer would also include an adhesion promoter and filler such as an epoxy resin and may also include solvents, fillers and an ultraviolet light absorber to indicate where the flow of the seal bond is taking place for purposes of inspection under an ultraviolet light. Other additives which act as adhesion promoters and fillers which are comparable to epoxy resin are also contemplated.
A method of producing a coated textile fabric for an air holding device in a vehicle restraint system is also disclosed, which comprises taking a base textile fabric having first and second surfaces, coating a first layer of an adhesive polyurethane onto the first surface of the textile fabric, and drying the first layer at an elevated temperature to form a first coating layer. The method further comprises coating a composite coating layer which includes a polyurethane and a polysiloxane onto the first coating layer and drying the composite coating layer at an elevated temperature to form a second coating layer. The method further comprises coating a third polyurethane layer onto the second composite coating layer and drying the third polyurethane layer.
A heat sealing die for sealing coated air bag fabrics is also disclosed, which comprises a heat sealing bar having a generally planar surface, and a combination of straight and arcuate cavities in the planar surface. The cavities are positioned in predetermined relative positions and orientations to form sealing beads on the coated air bag fabrics. The cavities each have an arcuate cross-sectional configuration to form sealing beads having corresponding cross-sectional configurations.